merge revision(s) c224ca4: [Backport #21172]

nagachika · nagachika · commit 726bff43b462 · 2025-03-16T18:02:45.000+09:00
Fix a race condition with interned strings sweeping.

	[Bug #21172]

	This fixes a rare CI failure.

	The timeline of the race condition is:

	- A `"foo" oid=1` string is interned.
	- `"foo" oid=1` is no longer referenced and will be swept in the future.
	- Another `"foo" oid=2` string is interned.
	- `register_fstring` finds `"foo" oid=1`, but since it is about to be swept,
	  removes it from `fstring_table` and insert `"foo" oid=2` instead.
	- `"foo" oid=1` is swept, since it has the `RSTRING_FSTR` flag,
	  a `st_delete` is issued in `fstring_table` which removes `"foo" oid=2`.

	I don't know how to reproduce this bug consistently in a single test
	case.
diff --git a/string.c b/string.c
@@ -344,6 +344,10 @@ fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t data, int exist
 
         if (rb_objspace_garbage_object_p(str)) {
             arg->fstr = Qundef;
+            // When RSTRING_FSTR strings are swept, they call `st_delete`.
+            // To avoid a race condition if an equivalent string was inserted
+            // we must remove the flag immediately.
+            FL_UNSET_RAW(str, RSTRING_FSTR);
             return ST_DELETE;
         }
 
diff --git a/version.h b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 7
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 131
+#define RUBY_PATCHLEVEL 132
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"

Original file line number	Diff line number	Diff line change
`@@ -344,6 +344,10 @@ fstr_update_callback(st_data_t key, st_data_t value, st_data_t data, int exist`
`344`	`344`
`345`	`345`	`if (rb_objspace_garbage_object_p(str)) {`
`346`	`346`	`arg->fstr = Qundef;`
	`347`	+ // When RSTRING_FSTR strings are swept, they call `st_delete`.
	`348`	`+ // To avoid a race condition if an equivalent string was inserted`
	`349`	`+ // we must remove the flag immediately.`
	`350`	`+ FL_UNSET_RAW(str, RSTRING_FSTR);`
`347`	`351`	`return ST_DELETE;`
`348`	`352`	`}`
`349`	`353`